The invention is directed to improvements in electromagnetically actuatable valves.
An electromagnetically actuatable valve is already known from U.S. Pat. No. 4,666,087 in which a valve needle opening outward is supported in a guide bore and actuated in the opening direction counter to a valve needle spring by an armature. In this valve, not only does the friction of the motion of the valve needle lead to hysteresis errors in triggering the valve, but the electromagnet also requires high triggering power in actuating the valve needle, to overcome the force, of the valve needle spring, and must therefore be made larger for this purpose. In addition, the valve needle in the guide bore is always guided by the valve needle it contacts the guide bore unilaterally, resulting in an uneven fuel stream emerging from the fuel injection valve, leading in turn to poorer fuel preparation and poorer uniformity of distribution to the various cylinders of the internal combustion engine. In response to this problem, a hydraulically centered system has been developed, but because of the friction and the unfavorable position of the centering forces, centering that is adequate for all requirements is attainable by the hydraulic orienting forces only with difficulty. Although the pressure drop of the hydraulic centering does stabilize the static quantity, this stabilization is not actually needed, the disadvantage being the lack of pressure for preparing the fuel predominates. In a system having a conical stop plus hydraulic centering, the centering of the conical stop is not adequate until the length of the system is relatively great in proportion to the sealing diameter. Especially in low-pressure single-point valves (having a large opening cross section), this means that the mass to be moved is large, making the valve vulnerable to transverse acceleration. Compensating for this by plastic deformation in the axial direction is made more difficult by the low spring rigidity, because of the great length.